No, it's obviously not the only place it can go, but we've been led to believe the purpose of one of the newly purchased ferries is to do the Hua Hin/Sattahip run. I'm sure there has been somebody, but I personally have never heard of anybody needing/wanting to travel from Hua Hin to Sattahip.

The route is due to start this month, I'm just baffled without sensible promotion, where they think the passengers will come from.

The Gov could use it for personnel transport. Big navy presence in both Sattahip and Hua Hin area, with personnel going back and forth frequently, especially officers I would think. Just a thought. Pete

Governments are instituted among Men, deriving their just powers from the consent of the governed. Source

Well the Royal Navy is investing 2 billion to accommodate ferries and cruise ships. It was a government statement that announcing the purchase of more ferries. I'd say it's quite easy to work out.
And I believe (I may be wrong) that a private company cannot have the word Royal in their name.